For the purpose of preventing intrusion of foreign matters such as dust into a joint and preventing leakage of a grease sealed inside the joint, a bellows boot is mounted to a constant velocity universal joint used for power transmission in automobiles and various industrial machineries.
As illustrated in FIG. 3, the boot of this type includes a large diameter section 33 fixed to an outer race as an outer joint member of the constant velocity universal joint, a small diameter section 34 fixed to a shaft extending from an inner race as an inner joint member of the constant velocity universal joint, and a bellows section 35 provided between the large diameter section 33 and the small diameter section 34 and including valley portions 36 and peak portions 37 that are formed alternately with each other. The large diameter section 33 and the small diameter section 34 are fixed by boot clamps mounted thereto.
The constant velocity universal joint has such functions as to be rotated while forming an operating angle and rotated while plunging in an axial line direction. Thus, the boot mounted thereto has a bellows shape so as to secure such flexibility as to be capable of following behavior of the constant velocity universal joint.
That is, the bellows boot is deformed so as to follow movements of the constant velocity universal joint, such as formation of an operating angle or plunging. Further, examples of the boot for a constant velocity universal joint include a rubber boot using chloroprene rubber or the like, and a resin boot using a thermoplastic elastomer material. The resin boot is excellent in durability in comparison with the rubber boot, and hence has been more widely applied.
In an example of the resin boot of this type, clearances between the peak portions 37 and the valley portions 36 connected thereto are substantially uniform, a radial step rate between the valley portions 36 and the peak portions 37 connected from the valley portions 36 toward a small diameter section side is set to fall within a range of from 26 to 36%, and thicknesses of the peak portions are set to fall within a range of from 60 to 100% of thicknesses of the valley portions connected to the peak portions 37 (Patent Literature 1). With this structure, such attempts are made as to enhance facility in folding of the bellows section, and prevent crack occurrence owing to abrasion of contact portions at the time of bending at wide angles.